(1) Field of the Invention
The present invention relates to the preparation of poly(1,4-dioxan-2-one) as a copolymer with a cyclic ester in a melt. In particular, the present invention relates to a reactive extrusion process for bulk copolymerization of 1,4-dioxan-2-one and the cyclic ester using an organometallic polymerization agent (catalyst or initiator), particularly a coordination insertion catalyst, to form a polymer with a high molecular weight with good control over molecular weight. In particular, the present invention relates to a reactive extrusion process for bulk copolymerization of 1,4-dioxan-2-one copolymerized with a limited amount of comonomer which is the cyclic ester, particularly a lactone or dilactone, using a coordination-insertion agent, to form an aliphatic copolyester with good control over molecular weights and conversion, and with improved thermal properties for use as biodegradable plastics.
More specifically, the present invention relates to a continuous extrusion polymerization process of 1,4-dioxan-2-one and the cyclic ester to produce high molecular weights at high throughputs. The present invention also relates to a continuous extrusion polymerization process of 1,4-dioxan-2-one copolymerized with a limited amount of the cyclic ester to produce high molecular weight aliphatic copolyester with fraction of the cyclic ester in the polymer of than 5 wt %, preferably 3 wt %, at high throughputs. The present invention also relates to the manufacture of semi-crystalline poly(1,4-dioxan-2-one) copolymer with improved thermal properties and thermal stability. The present invention also relates to compositions derived by reactive extrusion polymerization process, which are useful in making biodegradable articles and specially related to a unique intermediate that exhibits branching.
(2) Description of the Related Art
1,4-Dioxan-2-one is known to be polymerized readily in bulk (absence of any solvent) using organometallic or enzymatic catalysis such as tin (II) bis (2-ethylhexanoic acid), diethylzinc, triethylaluminium, Zn lactate and derivatives of Ti, Zr and Hg (Snapp, H. et al. U.S. Pat. No. 3,645,941, Bezwada, R. et al. U.S. Pat. No. 4,643,191, Schultz, H. U.S. Pat. No. 3,063,967, Bagget, J. et al. U.S. Pat. No. 3,391,126, Doddi, N. et al. U.S. Pat. No. 4,032,988, Kricheldorf, H. Macromol. Symp. 130: 393 (1998), Nishida, H. at al. J. Polymer Science: Part A: Polymer Chemistry 38: 1560 (2000)). However, as a result of the dynamic chemical equilibrium between 1,4-dioxan-2-one (PDX) and poly(1,4-dioxan-2-one) above the melting point of the polymer, conversion of monomer is typically limited to about 78%. Removal or recovery of unreacted monomer from the melt is difficult because of the tendency, given this dynamic equilibrium, of the polymer to depolymerize or lose molecular weight as the monomer is removed to maintain the equilibrium monomer content.
U.S. Pat. No. 5,717,059 describes a method for removing the PDX monomer from previously solidified polymerizing mixture without any adverse degradation reactions to form high molecular weight polymers. However, the time for removing the unreacted monomer from the polymerizing mixture was on the order of hours. The process used to manufacture high molecular weight 1,4-dioxan-2-one polymers is extremely time-consuming and cost-expensive.
Thermal stabilized poly(1,4-dioxan-2-one) polymers have also been prepared by end-capping the extremity of poly(1,4-dioxan-2-one) in the melt. However, after end-capping of the poly(1,4-dioxan-2-one) extremity by a chemical agent such as pyromellitic anhydride, the reacting mixture still contains a large amount of unreacted monomer, which has to be removed from poly(1,4-dioxan-2-one) and recycled, making the process economically unattractive (U.S. Pat. No. 5,652,331).
To permit commercial scale-up of the polymerization without adversely affecting process economics, it is necessary to provide an appropriate, inexpensive and easy process to manufacture thermal stabilized poly(1,4-dioxan-2-one) with conversion close to completion as well as a corresponding process for manufacturing it in order to achieve an inexpensive and integrated production with high volumes.
It is highly desirable to carry out the polymerization reaction in the melt rather than in solution for environmental concern and unfavorable economics related to the use of organic solvents. Further, bulk polymerization can be conducted in extruders, making it a continuous process. Polystyrenes and nylons have been produced commercially by polymerization in an extruder. A number of patents have evolved in the extrusion of these polymers; the process schematics and screw configurations vary considerably. The extruder screw configuration can improve yield, molecular weight, molecular weight distribution and product throughput.
Reactive extrusion is an attractive route for polymer processing in order to carry out various reactions including polymerization, grafting, branching and functionalization. Reactive extrusion polymerization involves polymerizing a liquid/solid monomer or pre-polymer within the residence time available in the extruder to form a high molecular weight melt.
The prior art has shown that extruders can be used for bulk polymerizations of monomers like methylmethacrylate, styrene, lactam, ε-caprolactone and lactide (Michaeli, W. et al., J. of Appl. Polymer Sci. 48:871-886 (1993); Kye, H., et at., J. of Appl. Polymer Sci. 52:1249-1262 (1994), U.S. Pat. Nos. 5,412,005 and 5,906,783). The economics of using the extruder for bulk polymerization are favorable when high throughputs and control of molecular weight are realized.
Low cost production and processing methods for biodegradable plastics are of great importance since they enhance the commercial viability and cost-competitiveness of these materials. Reactive extrusion is an attractive route for the copolymerization of 1,4-dioxan-2-one as well as its copolymerization, without solvents, to produce high molecular weight biodegradable plastics.
References cited and incorporated by reference in their entirety
US patent:Snapp, H. et al.U.S. Pat. No. 3,645,941Bezwada, R. et al.U.S. Pat. No. 4,643,191Schultz, H.U.S. Pat. No. 3,063,967Bagget, J. et al.U.S. Pat. No. 3,391,126Doddi, N. et al.U.S. Pat. No. 4,032,988Forschner; T.U.S. Pat. No. 5,717,059Forschner, T. et al.U.S. Pat. No. 5,652,331Bastioli, C. et al.U.S. Pat. No. 5,412,005Narayan R. et alU.S. Pat. No. 5,801,224Narayan, R. et al.U.S. Pat. No. 5,906,783Narayan, R. et al.U.S. Pat. No. 5,969,089Fritz, H. et al.U.S. Pat. No. 6,166,169Articles:Kricheldorf, H. Macromol. Symp. 130: 393 (1998)Nishida, H. at al. J. Polymer Science: Part A: Polymer Chemistry 38: 1560(2000)Michaeli, W. et al., J. of Appl. Polymer Sci. 48: 871-886 (1993)Kye, H., et al., J. of Appl. Polymer Sci. 52: 1249-1262 (1994)